Quantitative evaluation of Pinus nigra plantation and its effect on plant diversity and soil chemical properties of rangeland ecosystems

In this study, Pinus nigra forest plantation with an area about 10 hectares, located in Urmia airport was investigated. Sixteen 300 m² circular sample plots were set up with systematic random method in 50×50 m grids network. One 100 m² subplots, within the same plot, were established to record plant species and its cover. Soil samples in two depths (0-10 and 10-30cm) were taken in every other samples and soil factors including pH, soil organic carbon, total nitrogen, absorbable phosphorous were measured. Also a rangeland adjacent to plantation area was selected and three plots with 50 m distance spacing were laid out along a transect. Herbaceous species and soil factors were assessed in each plot similar to plantation area. The mean of diameter and height annual increment was calculated via dividing the diameter and height means by stand age till study time (40 years). Species richness and diversity indices were calculated in each plot. T-student test was used to test for significant differences between the means of indices and soil factors of two areas. Non-metric multidimensional scaling was applied to assess the rate of changes on the vegetation and soil chemical properties due to the plantation. Results showed that the mean diameter and height increment were 0.46 cm and 0.29 m,  respectively.Species richness and Shannon diversity indices considerably decreased in the plantation area. The average of soil organic carbon, total nitrogen in the control area were more than those of the plantation area. Light, soil organic carbon, total nitrogen and absorbable phosphorous were the most important factors influencing the distribution of plant species. Generally, it is suggested that this species would not be planted in the wide regions and in the region in which it’s necessary to conserve plant composition and diversity.